When handling or treating plastic material, which in the form of raw material contains substances that may be toxic or may cause allergy symptoms of the work-people, the material, up to the time it is fed into the machine, must be packed in a packaging material preventing the emission of said substances. At the time of feeding the material into the machine, the packages are usually opened manually, and even if this takes place with great care there are great risks that sufficient amounts of said substances shall be emitted in order to cause injuries or inconveniences to the work-people.